1. Field of the Invention
The present invention relates to a radio apparatus and an antenna device for a mobile radio system, and in particular to a radio apparatus having a plurality of housing sections and an antenna device adapted for such a radio apparatus.
2. Description of the Related Art
Most of radio apparatuses such as mobile phones in recent years have a configuration in which two housing sections are movably connected in such a way as to be open and closed to each other, so as to meet the requirement for multiple functions and high performance and the requirement for downsizing and thinning at the same time. The radio apparatus connects the two housing sections by using a flip type structure, a flip type structure with a two-axis hinge (may be called a swivel type) or a slide type structure. The above flip type structure and the swivel type structure has a hinge section and the two housing sections are rotatably connected to each other through the hinge section.
Meanwhile, most of antenna devices of radio apparatuses such as mobile phones are of a built-in type in the housing rather than a type to be extended out of the housing and used such as a whip antenna. The radio apparatus can raise an aesthetic or operational aspect by using such a built-in type antenna device. As described above, however, the radio apparatus is required to have multiple functions and high performance and to be downsized and thinned at the same time. Thus, the antenna device is required to give necessary performance while being arranged in limited space inside the housing.
In order to meet the above requirement, a mobile radio apparatus is constituted by including an antenna in a hinge section as disclosed in Japanese Patent Publication of Unexamined Applications (Kokai), No. 2007-88692. The mobile radio apparatus of JP 2007-88692 is constituted by a first housing section and a second housing section rotatably connected to each other through a hinge section. A hinge core forming a hinge axis is arranged in the hinge section.
According to JP 2007-88692, the above hinge core is constituted by including a first member and a second member connected to each other. The first member is mechanically fixed to the second housing section and electrically connected to a circuit board included in the second housing section. The second member is mechanically fixed to the first housing section but not electrically connected to a circuit board included in the first housing section. The first member is made of conductive material such as metal and is shaped to be almost cylindrical or columnar, and so is the second member. Due to the above configuration, the hinge core can be fed from the circuit board included in the second housing section as an antenna element while not being electrically connected to the circuit board included in the first housing section.
In the mobile radio apparatus of JP 2007-88692, the whole hinge core forming the hinge axis is constituted by the conductive members and is fed as the antenna element. According to the paragraph “0026” of the specification of JP 2007-88692, the hinge core is constituted by the conductive members such as metal and is shaped to be almost cylindrical or columnar. The first member and the second member are on the side of the second housing section and on the side of the first housing section, respectively, and are mechanically connected to each other in such a way as to rotate coaxially. The hinge core includes a mechanism configured to provide retention force for a click feeling, and a mechanism configured to provide rotation force for an unaided rotation.
A spring may be arranged in an axial direction of the rotation so as to give rotational resistance, as an example of the above “mechanism configured to provide rotation force for an unaided rotation”. In general, the spring is made of metal and is conductive, and may thereby affect an antenna characteristic upon changing its shape depending upon an open/closed state determined by the rotation between the two housing sections (e.g., an angle between the two housing sections of the flip type mobile phone). As the open/closed state usually changes in accordance with the purpose of use of the radio apparatus, it is not preferable for the antenna characteristic to be affected as described above.